1. Field of the Invention
This invention is related to the field of integrated circuits, and more particularly to the operation of and communication between elements of an integrated circuit operating at independent frequencies and/or voltages.
2. Description of the Related Art
Typically, the regulation of operating voltage for integrated circuits, such as microprocessors, may be performed by circuitry located on the motherboard, external to the IC, due in part to requirements for large values of capacitance which may consume inordinate amount of real estate on an IC die. Power at the voltage level of the output of a voltage regulator may be supplied to the internal circuitry including the processor cores of the IC through several package pins. This may be done in part to reduce the current handling requirements for any given pin and/or traces leading thereto. Generally, the supply lines may be internally connected so that the cores and other elements operate at a common voltage level.
Typically, complex logic core designs produce large quantities of heat at certain points within the IC, esp. at high clock frequencies. The packaging of an IC along with the device and system cooling mechanisms may determine the maximum frequency at which the IC may operate without exceeding its specified maximum operating temperature at the points where heat generation is most pronounced. An IC manufacturer may specify a maximum package temperature for a specific device at which it will continue to function both correctly and reliably.
Since complex ICs such as microprocessors tend to be expensive, it is typically desirable to protect them from damage due to overheating. Temperature sensors are often located in various places within systems containing complex ICs to measure the ambient temperature at that position. Due to the method commonly used to incorporate complex ICs into systems such as soldering to a motherboard or socketing to a motherboard, and the direct attachment of heat sinks and/or other cooling apparatus to the chips, temperature sensors are generally found in locations other than the IC itself. Therefore, the temperature of the IC package must commonly be extrapolated from an actual temperature measurement at some point remote from the surface of the IC. The resulting case temperature estimate may be significantly above the actual temperature of the IC if conservative algorithms are used to perform the estimation.
A typical system may use the estimated package temperature of the IC to control power to the entire system or at least to the IC. For example, the output of the temperature sensor may be compared to a “trip point” value, and when this value is reached, a signal may be generated that causes the system power supply to shut down. Such a system may indeed protect the IC, but may also inconvenience the user who is frequently given no advanced warning that a shut down is forthcoming and who may have entered significant amounts of data without recently saving it to persistent storage. Also, as noted above, all such shut downs may not be necessary since the mechanism may activate based on a conservative estimate of the actual temperature of the chip.
To reduce the potential for user data loss, systems may employee a second trip point circuit configured to trigger at a temperature somewhat lower than the shut down temperature. In such a system, the lower temperature circuit may be used to initiate action that would inform the user that a system shutdown is imminent, and that he should take appropriate actions to secure any unprotected data. While this scheme may help protect user data, it may also produce a significant nuisance if temperatures wander into the range between trip points without actually reaching the shutdown point. In any case once the shutdown limit has been reached, the user is without the use of his system until such time that it cools down sufficiently and can be restarted.